There have recently been developed digital record discs for recording data signals such as audio signals or image signals and record disc reproducing apparatus for reproducing the recorded data. A digital record disc stores digital data intended for high density recording in the form of a spiral bit string on one side of the disc and reproduced through reading the bit string by means of an optical pickup using laser beams. Moreover, the record disc reproducing apparatus is used to read the recorded data by causing the optical pickup to follow the bit string recorded on the digital record disc by a tracking control system and to process the read-out signal in a predetermined manner to convert the signal into the original analogue signal for example, an audio or video signal as an output.
As is well known, the digital data and address data indicating the address of the digital data is written to the program area of the digital record disc. For instance, in a CD (compact disc) type digital record disc (hereinafter called simply a disc), digital data such as audio signals in a digital form and their digital data track numbers, indexes and addresses, and address data indicating absolute time after the reproduction of the disc is started, are recorded.
A record disc reproducing apparatus for the CD type disc is provided with high speed movement of the pickup by performing fast-forward or fast-reverse of the pickup to select and reproduce a desired digital data, and an address search function to perform the automatic search for the desired address data within the enormous amount of data on the disc.
When the fast-forward or fast-reverse operation button or key has been operated, the pickup is correspondingly moved in an outward or inward radial direction of the disc at high speed by a pickup carriage motor. When the search operation button or key has been operated with the prior designation or presetting of the desired address of the program recorded on the disc, the high speed pickup is automatically moved until the desired address is read out.
To ensure that the search function can be quickly made by designating only the track number and the index on the disc, Table of Contents data (hereinafter called TOC data) indicating the digital data on the starting addresses (that is, absolute time) of the digital data to which each of the track numbers is allotted, are recorded in the read-in area thereof. In other words, the record disc reproducing apparatus stores the TOC data in the lead-in area and the search function is carried out by automatically referring to the starting address corresponding to the track number designated. As a result, the digital data can readily be reproduced with ease.
As for the digital data recorded on the CD type disc, a prescribed number of frames constitutes one data block, and are accompanied by prescribed units of subcodes in addition to the data converted from audio signals in the form of pulse code modulation (PCM). Among them, a subcode Q is address data for the recorded data and has a format shown in FIG. 1.
One unit of the subcode Q reproduced in the program area is, as shown, formed with the data reproduced in the order of the following items:
(1) S.sub.0, S.sub.1 : 2 bits synchronous pattern data section indicating the start of the subcode Q;
(2) CNT: 4 bits control data section distinguishing between two channel program and four channel program, and indicating a presence or an absence of pre-emphasis and a permission or a prohibition of copying;
0 0 x 0: 2 ch., emphasis OFF PA1 1 0 x 0: 4 ch., emphasis ON PA1 0 0 x 1: 2 ch., emphasis OFF PA1 1 0 x 1: 4 ch., emphasis ON PA1 x x 0 x: prohibition of copying PA1 x x 1 x: permission of copying PA1 (3) ADR: 4 bits mode data section indicating the data PA1 Mode 1 (BCD 1): Address Mode PA1 Mode 2 (BCD 2): Disc Catalogue Number Mode PA1 Mode 3 (BDC 3): Special Information Mode
(4) MNR: 8 bits (2 figures in BDC) program number index data section;
(5) X: 8 bits sub-index data section of the program;
(6) MIN: 8 bits first "minute" data section indicating the order of "minute" within the time elapsed since the reproduction of the prescribed program number was commenced (hereinafter referred to as relative time);
(7) SEC: 8 bits first "second" data section indicating the order of "second" within the relative time;
(8) FRAME: 8 bits first decimal place of "second" data section indicating the order of decimal of "second", dividing one "second" with prescribed digit number, e.g. 75, within the relative time;
(9) ZERO: Section composed of 8 bits representing digital 0;
(10) AMIN: 8 bits second "minute" data section indicating the order of minutes within the time elapsed since the reproduction was started from the read-in area (hereinafter referred to as absolute time), which represents the location or the address of the prescribed data;
(11) ASEC: 8 bits second "second" data section indicating the order of seconds within the absolute time;
(12) AFRAME: 8 bits second decimal place of "second" data section indicating the order of decimal place of "second", dividing one "second" with the prescribed digit number, e.g. 75, within the absolute time; and
(13) CRC: 16 bits error check code data section for the subcode Q.
The subcode Q formed with the above format is extracted by the record disc reproducing apparatus and not only the state in which each data (for instance, (MNR), (X), (MIN), (SEC)) is reproduced but also the mode in which the pickup is fast carried are displayed by the display unit of the record disc reproducing apparatus, so that the desired address can readily be attained.
For the search function to be carried out as quickly as possible, the pickup must move more quickly than the fast-forward or fast-reverse operation function are accomplished in the radial direction of the disc; however, in conventional apparatus, the address data on the disc becomes unreadable during such high speed pickup movement, and the search function cannot be carried out.
To avoid this problem, a record disc reproducing apparatus capable of making a search at a higher speed has been constructed so that address data is made to stop for a prescribed period of time during which the data is readable after the pickup is moved a prescribed distance at a speed higher than the fast-forward or fast-reverse operation modes, and this operation is repeated until the desired address is attained.
With the above arrangement, an address of a track where the pickup is located is read out each time the pickup is moved thereon at high speed during the search. The reading out time of addresses is unnecessarily wasted when an address to be reached is far from the address of the track corresponding to the position of the pickup (hereinafter referred to as the reproduction address).
Moreover, when dust or a crack on the disc makes the address data unreadable, the record disc reproducing apparatus keeps attempting to read address data until all the address data is read out. This means that extra time is required before the completion of the search.